Dietary Flavonoids Scavenge Hypochlorous Acid via Chlorination on A- and C-Rings as Primary Reaction Sites: Structure and Reactivity Relationship

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Abstract
Dietary flavonoids are known as scavengers of reactive oxygen species such as hypochlorous acid. In spite of abundant scavenging capacity data reported, few reports have addressed the relationship between the scavenging capacity and structures of different flavonoids. We characterized the reaction products of five flavonoids (apigenin, quercetin, naringenin, ampelopsin and epicatechin) with hypochlorous acid and found that primary chlorination reaction occurred on A ring (C6 or C8) and/or C rings but not on B rings. Correlation of the hypochlorous acid scavenging capacity (IC50 values) and the structural features of flavonoids revealed that the hydroxyl groups in the A ring and B ring can enhance the scavenging capacity whereas the C(2)C(3) double bond has negative impact to the HClO scavenging capacity. Combining the SAR analysis and chemical study, we proposed that reaction mechanism between flavonoids and HClO should be electrophilic substitution reaction. Density functional theory (DFT) results are in consistent with the selectivity of chlorination on the flavonoids. Our findings highlight the importance of considering specific reactive oxygen species when measuring radical scavenging capacity of dietary antioxidants.
Funding Information
  • Ministry of Education - Singapore (MOE2014-T2-1-134)

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